By the way: our team at Sinovo has tested some adapters. The report ist shown here:
http://www.sidiary.de/Sitecom-USB-Seriell-293.asp (at this time in german only, sorry).
They had figured out, that some adapters could cause problems unless they need the newest drivers for it (usually you can get them at the manufacturers homepages), and the best one is indeed the Sitecom CN 104
